Selecting/highlighting Text Problem

I am using Backtrack 5. As it is based on Ubuntu 10.04 I decided to ask my question to here: I'm having problems selecting text with my mouse. For example when I try to rename a folder, sometimes I can successfully highlight the text but when I release the mouse button, it is no longer highlighted. Sometimes I can't even successfully highlight the part of the text that I want. It highlights more or less of the text then actually selected. First I thought it was a problem caused by my mouse, however, I tried another mouse and the problem continues. This problem really bothers me while surfing on the net. Could you please help me?